Next generation mobile devices implement a plurality of wireless technologies to support voice communications and data communications. In particular, high-speed data technologies such as GPRS, EDGE, and IEEE 802.11a/b/g/n WLAN technology facilitate data communications. WLAN technology is a power hungry technology; hence battery power limitations remain a constraint and techniques to improve battery power and/or power efficiency are being pursued. Often power-saving mechanisms are an important differentiating factor between different handset vendors.
The IEEE 802.11 standard specifies a Power-Save (PS) mechanism for use by WLAN stations. This mechanism is shown in FIG. 1 and operates as follows:                The WLAN node informs the access point (AP) that the node is entering a Power-Save (PS) mode during which the AP is able to buffer packets that are addressed for this node.        The AP periodically sends beacons which include a traffic indication map (TIM) informing the nodes that are in PS mode whether there are buffered packets for these nodes or not.        If a node learns from the TIM that the AP has buffered packets for it, the node transmits a Power-Save Polling (PS-Poll) frame after a time interval. The duration of the time interval depends on the number of active-mode stations (STAs) present in the network, as well as the number of PS-mode STAs informed via the TIM because transmission of PS-Poll frame from the node competes with other transmissions from other nodes and follows WLAN CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) procedure        Once the AP receives the PS-Poll, the AP responds with an acknowledgment (ACK) and thereafter sends a buffered data packet to the corresponding STA. The AP can also send a buffered data packet directly to the STA immediately after receiving a PS-Poll (without sending an ACK first). In either case, the “more data bit indicator” of the sent data packet header could be set to “1” if there are more buffered packets for this node, or “0” if there are no more packets left in the buffer for this node. The node/STA will transmit another PS-Poll if more data bit is set to “1” and the process continues.        
The above PS-Poll approach is able to save STAs significant power as they can turn off their radios from time to time without losing their data service. However, this PS-Poll approach also suffers from longer delays for the downlink data, which may potentially be a performance pitfall for Quality of Service (QoS) applications, such as Voice over IP (VoIP) or real-time audio/video broadcasting, because these applications usually demand stringent delay bounds for their data packet delivery. For example, a typical VoIP traffic flow demands to have a 30 ms delay bound for its packet. If a WLAN beacon interval is set at a typical value of 100 ms, it is quite likely that the buffered VoIP packet at the AP will experience a delay bound beyond 30 msec.
In order to satisfy the delay bound requirements of QoS flows, a periodic PS-Poll mechanism has been proposed and implemented. Using this mechanism, a PS mode station may periodically send out a PS-Poll to the AP node asking for buffered data packets even if the station did not receive an indication from the AP that it has the buffered data. The operation of periodic PS-Polling is illustrated in FIG. 2.
As shown in FIG. 2, the STA sends periodic PS-Poll for every interval time of Ti. If the AP does not have buffered data for the STA, the STA is idle after receiving the PS-ACK from the AP. In many AP implementations, if the AP does not have data to send to the STA, instead of doing nothing, the AP will send a QoS-NULL packet to tell the station about its current buffer status. In either case, after a timeout of To, it is reasonable to let the STA go to sleep mode if the STA does not receive anything during that time. If on the other hand, the AP has buffered data for the STA, then the AP will send a single data packet (from the buffered data) to the STA. If the AP has more than one buffered data packet, the data packet will have a “more data bit indication” set so that the STA will continue to poll for the next buffered data packet. Although the above-mentioned periodic PS-Poll mechanism can help STAs in WLAN to partially solve the delay bound problem due to QoS flow, improvements to periodic PS-polling are possible.